1. Field of the Invention
The present general inventive concept relates to a piezoelectric inkjet head, and more particularly, to a restrictor having a structure to prevent a back flow, and a piezoelectric inkjet head including the restrictor.
2. Description of the Related Art
Inkjet heads are devices used to form color images on printing mediums such as paper and fabric by firing droplets of ink onto a desired region of a corresponding printing medium. Inkjet heads can be classified into various types depending on the ink ejecting method to be used. For example, a thermal inkjet head generates ink bubbles by using heat and ejects the ink by utilizing the expansion of the bubbles, and a piezoelectric inkjet head ejects ink using a pressure generated by deforming a piezoelectric material.
FIGS. 1 and 2 illustrate a general structure of a conventional piezoelectric inkjet printhead.
Referring to FIGS. 1 and 2, an ink channel is formed in first to third channel plates 10, 20, and 30. The ink channel includes an ink inlet 61, a manifold 62, a plurality of restrictors 63, a plurality of pressure chambers 64, and a plurality of nozzles 65. Piezoelectric actuators 40 are formed on the first channel plate 10 respectively corresponding to the pressure chambers 64. The manifold 62 is formed in the second channel plate 20 to receive ink from an ink tank (not illustrated) through the ink inlet 61 and supply the ink to the respective pressure chambers 64. The restrictors 63 are formed in a top surface of the second channel plate 20 for respectively connecting the manifold 62 to the pressure chambers 64. The pressure chambers 64 store ink that is to be ejected. The pressure chambers 64 are formed in the second channel plate 20. The pressure chambers 64 are arranged at one side or both sides of the manifold 62. The pressure chambers 64 change in volume due to operation of the piezoelectric actuators 40, and as a result, the pressure in the pressure chambers 64 changes. Thus, ink can be ejected from or introduced into the pressure chambers 64 due to the pressure change. Portions of the first channel plate 10 covering the pressure chambers 64 are referred to as vibration plates 12. The vibration plates 12 deform by pressure applied from the piezoelectric actuators 40. The nozzles 65 are formed through the third channel plate 30 and are respectively connected to the pressure chambers 64.
The conventional piezoelectric inkjet head illustrated in FIGS. 1 and 2 operates as follows. When a driving signal is applied to the piezoelectric actuator 40, the piezoelectric actuator 40 deforms the vibration plate 12 to reduce the volume of the pressure chamber 64. As a result, the pressure in the pressure chamber 64 increases, and thus, ink is ejected to the outside of the pressure chamber 64 through the respective nozzle 65. Thereafter, when the piezoelectric actuator 40 and the vibration plate 12 both return to their original shapes, the volume of the pressure chamber 64 increases, and the pressure in the pressure chamber 64 decreases. Therefore, ink can be introduced into the pressure chamber 64 from the manifold 62 through the restrictor 63 to refill the pressure chamber 64.
However, in the conventional piezoelectric inkjet head, ink can flow back from the pressure chamber 64 to the manifold 62 through the restrictor 63 when the actuator 40 operates to eject ink from the pressure chamber 64 through the nozzle 65.
Furthermore, when ink flows back from the pressure chamber 64, pressure waves are transmitted from the pressure chamber 64 to neighboring pressure chambers 64 through the manifold 62. This phenomenon is referred to as a cross talk. The cross talk causes unstable meniscuses of ink in the nozzles 65 of the neighboring pressure chambers 64, and thus, the speed and volume of ink droplets ejected through the nozzles 65 are deviated. In addition, less ink is ejected through the nozzles 65 due to a back flow of ink.
Therefore, the restrictors 63 should have a structure to prevent a back flow of ink, as well as providing an ink path allowing inflow of ink from the manifold 62 to the pressure chambers 64. In other words, a back flow of ink can be easily prevented when the restrictors 63 have a small cross section. However, in this case, ink may be insufficiently filled into the pressure chambers 64 through the restrictors 63. In the conventional piezoelectric inkjet head, the restrictors 63 have a fixed structure (that is, the cross sectional area of the restrictors 63 is fixed), and thus, it is difficult to satisfy these requirements using the restrictors 63.